Back in March of last year scientists reported finding a "zombie fungus" that was affecting ant colonies in Brazil, the details of which sounded something straight out of a George A. Romero film. Nicknamed the "zombie-ant fungus", it invades an ant's brain and takes control, forcing the ant march to its death at a mass grave near the ant colony. Once there, fungal spores erupt out of the ant's head in an effort to infect a passing victim. But just when you thought things couldn't look more grim, it now appears that a parasite has come to the ants' rescue — one that's waging a war against the disease itself.

The parasite was discovered by a team led by David Hughes of Penn State University. The research is helping scientists understand how entire ant colonies have been able to survive the onset of the zombie-ant fungus. It turns out that the newly discovered parasite is itself a fungus — a hyperparasitic fungus that specializes in attacking the very parasite that turns the ants into zombies.

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According to Hughes, the parasite effectively castrates the zombie-ant fungus such that it cannot spread its spores. Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading its spores, fewer of the ants contract the infection. And it appears that the parasite is winning.

The scientists report that only about 6.5% of the spore-producing organs of the zombie-ant fungus remain viable after infection by the hyperparasitic fungus. What this means is that, even though there are many infected ants in the colony, only a few of the spores of the zombie-ant fungus will become mature and able to infect healthy ants. Hughes' research indicates that the danger to the ant colony is much smaller than the high density of zombie-ant cadavers in the graveyard might suggest.

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To help them in their research, the scientists created a model that revealed details of the interactions between the fungus-infected ants and the parasite-infected zombie ant fungus. Scientists had previously observed that ants can defend themselves against diseases by grooming each other and by changing their interactive behaviours. But the Hughes-led study now indicates that a third-party can also tilt the balance in the war against infection.